This is rather odd. I can make it happen too. The menu starts again when I connect the PC by USB again.
If I also have a Wifi ssh connection, that hangs too, so I cannot run any commands to investigate what is happening.
However, I think I have determined it is not to do with the menu, as if I kill the menu but keep a Wifi ssh connection, that hangs too and starts again, when I reconnect the USB.
Andy, I think it must be something to do with usb networking. It doesn't happen completely consistently. Sometimes when I pull the USB connection out, the Wifi ssh connection just hangs for a while. Sometimes it seems to hang permanently (until the USB is reconnected).
I don't know why the when the menu is running it responds as far as the key beep, but does not display the new screen.